The present invention relates to the attenuation of common mode electromagnetic noise in the vicinity of electrical power, audio signal, and video signal cables, especially noise frequencies below 1 MHz, and in particular relates to attenuation of such noise in consumer and professional audio and video electronics cables.
Although electrical power utility companies attempt to provide a reasonably pure alternating current power supply to their customers, ordinary electrical power circuit wiring acts as an antenna and commercial line power thus is affected by electromagnetic noise originating from many sources. Much of such noise found in electrical power lines is related to the line frequency and its related harmonics and sub-harmonics, and some of such noise is caused by transient currents resulting from power source phase variations brought on by changing loads imposed by motors, etc. Imbalances in the utility transformer circuit of the power line can cause transient direct currents superimposed on the alternating current. All of the above can result in noise in the power line and affect the ideal sine wave form of the alternating current in the power line.
Noise may also be conducted into a power line from consumer electronics or electrically-powered devices. Changing power source loads imposed by power supplies in computers, digital audio electronics, video circuits, amateur radio devices, citizens, band transceivers, and household appliances all can contribute to changing electromagnetic flux fields whose lines of force are cut by a power cable located in the vicinity of such a device, and transient voltages can be fed back into the power source directly from electrical and electronic devices.
The performance of electronic devices can be noticeably affected by the presence of variations in the voltage wave form in the line power supply. In particular, the output of audio and video reproduction devices can be noticeably degraded by noisy power line voltage wave forms. Ferrite materials are commonly used to attenuate common mode circuit noise, as mentioned in Matsui U.S. Pat. No. 4,873,505, Fujioka U.S. Pat. Nos. 4,882,561 and 4,972,167, and Nakano U.S. Pat. No. 4,885,559. It is thus known to place a quantity of magnetizable material in the form of powdered ferrite carried in a matrix of an elastomeric material in the vicinity of a power cable, as mentioned in those patents. A problem with such use of ferrite materials is that the permeability of the material works well only in the higher frequency ranges of 10 MHz to 100 MHz. The ferrite material performs poorly at frequencies between 0 and 1 MHz with respect to attenuating common mode noise in an electrical conductor cable.
It is well known to provide shields of electrically conductive material and layers of ferro-magnetic material surrounding electrical conductor cables located in the vicinity of transient voltages, as disclosed, for instance, in Rogers, U.S. Pat. No. 5,349,133, Baigrie, et al., U.S. Pat. No. 4,816,614, and Palmer U.S. Pat. No. 5,548,082. Such shielding, however, is somewhat costly and is not particularly convenient to use, and it has not been particularly effective in the frequency range from 0 to 1 MHz.
While it is also known to use sophisticated and expensive electronic circuits in the power supply circuits of audio and video electronic devices to eject harmonics and other signals to arrive at a clean internal power supply output, what is desired is a device and a method for its use at a relatively low cost to provide noticeable improvement in the performance of electronic devices by attenuating the effects of electromagnetic noise on power cables, audio signal cables, and video signal cables.
The present invention provides an answer to the aforementioned need for a method and a device of relatively low cost for attenuating noise caused by incidental electromagnetic fields and stray or transient currents in alternating current cables and audio or video signal cables, through placement of a permanently magnetized magnet, preferably of relatively high field strength, in close proximity to an electrical conductor cable in which it is intended to attenuate electromagnetic noise from a desired signal. Use of the method and apparatus of the invention results in noticeable improvement in the audio and video output performance of electronic devices.
According to the present invention a permanent magnet may preferably be placed and retained as closely practical alongside an electrical conductor cable, with an axis extending between the poles of the magnet oriented generally parallel with the length of the cable.
In accordance with the method of the present invention a permanently magnetized magnet may be so located and held in proximity to a cable providing main power to an electronic device, a cable carrying alternating current power between a power panel and an electronic device, or an analog or digital signal conductor cable, to produce improvement in the perceived output quality of audio equipment such as CD players and phonographs, or of DVD playback equipment and other video reproduction electronic equipment.
In a device that is one embodiment of the invention a pair of permanently magnetized magnets may be similarly oriented magnetically and kept in place on opposite sides of a conductor cable, with quantities of magnetically permeable magnetic material, such as an appropriately formed sheet of iron, extending around the magnets and the cable to shape a magnetic field surrounding the cable.
Preferably a permanently magnetized magnet and such a piece of magnetic material is contained in each part of a two-part case, which is held together around a cable by suitable fasteners.
In a device that is one embodiment of the invention permanently magnetized material of one or more permanent magnet elements may itself be of a shape to enclose and surround a portion of the length of a cable of two or more electrical conductors, with axes of polarity of such permanent magnet elements extending generally parallel with the portion of the conductor cable along which the permanently magnetized material is located.
In another embodiment of the invention one or more permanent magnets may be located in proximity to a cable, with the poles of the magnet located in such a manner that the lines of force extend predominantly transversely with respect to a longitudinal axis of the cable, but this orientation apparently is less effective than having the axes of polarity parallel with the longitudinal axis of the cable.
While it is not fully understood how the method and apparatus of the present invention provide the desired attenuation of spurious and transient signals imposed on an electronic signal of a predetermined desired wave form and frequency, it appears that the performance of the invention is improved when the field strength of the permanent magnet is greater, and particularly when the field strength in the vicinity of the cable with which such a device according to the present invention is used is at least 1000 Gauss.
It has been found that the present invention is apparently effective with respect to use of a device incorporating the invention on conductor cables including parallel pairs of conductors carrying alternating current, parallel pairs associated with a parallel ground conductor, twisted pairs of conductors, and shielded coaxial pairs of conductors.
The foregoing and other objectives, features, and advantages of the invention will be more readily understood upon consideration of the following detailed description of the invention, taken in conjunction with the accompanying drawings.